Metformin-Insulin versus Metformin-Sulfonylurea Combination Therapies in Type 2 Diabetes: A Comparative Study of Glycemic Control and Risk of Cardiovascular Diseases in Addis Ababa, Ethiopia

Objective This study aimed to compare glycemic control and risk of cardiovascular outcomes of metformin-insulin versus metformin-sulfonylurea combination therapies in type 2 diabetes mellitus. Methods We conducted a comparative cross-sectional study in five tertiary level hospitals in Addis Ababa, Ethiopia. We enrolled 321 patients with type 2 diabetes mellitus who were on continuous treatment follow-up on either metformin-insulin or metformin-sulfonylurea combination therapy. We interviewed the participants and reviewed their medical records to investigate medication efficacy, safety, and adherence. The primary outcome measure was glycemic control and the secondary outcome measures were composite cardiovascular outcomes. Results Of the total participants enrolled, 50.5% (n = 162) were those who received metformin-insulin and 49.5% (n = 159) metformin-sulfonylurea combination therapies for a median of 48 months follow-up. The reduction of Hb1Ac levels was comparable between the metformin-insulin (-1.04 ± 0.96%) and metformin-sulfonylurea (-1.02 ± 1.03%), p = 0.912. Patients who received metformin-sulfonylurea had 4.3 times more likely to have achieved target HbA1c level compared to those who received metformin-insulin, p < 0.001, adjusted odds ratio (AOR) with 95% CI = 4.31[1.79-10.32]. Risk of composite cardiovascular outcomes was higher in metformin-insulin group (40.5% versus 34.0%), p = 0.021. Co-morbidities, body mass index, systolic blood pressure, and HbA1c had a significant association with composite cardiovascular outcomes. Reductions of bodyweight, HDL-C, LDL-C, triglycerides levels, and microvascular complications were different between the two groups, p < 0.05. Conclusion High proportion of patients who received metformin-sulfonylurea achieved target HbA1c level and had less composite cardiovascular outcomes compared to those who received metformin-insulin. However, these findings have to be confirmed with randomized control trials to determine risks associated with insulin use, while efficacy is maintained as second-line treatment in patients with type 2 diabetes mellitus.